Update Snappy Compression/Decompression

[mhusinsky]

it appears that IronSnappy (a managed library) has been deprecated in favour of IronCompress, which uses native Snappy libraries.

Updating to the new version might also help with #10 as it appears to allow for using pre-allocated buffers

[mhusinsky]

IronCompress looks promising, as it can be provided an ArrayPool as a memory backend.

However, the decompression result, which contains the rented buffer, exposes this as a Span. Not sure if there are ways to create a VL Image from this without additional copies...